In response to recent social demands and trends in the context of energy and environment problems, fuel cells capable of operating even at ordinary temperature and obtaining high output density have attracted attention as a power supply for an electric car and a stationary power supply. A fuel cell is a clean power generation system in which an electrode reaction product is water in principle and which reduces the load on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power supply for an electric car because it operates at relatively low temperature.
A polymer fuel cell includes a membrane electrode assembly (MEA, hereinafter referred to as MEA) having an electrolyte membrane, catalyst layers provided on both surfaces of the membrane, gas diffusion layers (GDLs), and so on. A plurality of MEAs are stacked with separators being disposed therebetween to constitute a fuel cell.
As a technique of forming electrode catalyst layers on both surfaces of an electrolyte membrane when manufacturing an MEA, a method of applying catalyst ink onto the electrolyte membrane is known (see, for example, Patent Literature 1). In the method described in Patent Literature 1, an outer peripheral frame is attached to an electrolyte membrane such as to clamp an outer peripheral portion of the electrolyte membrane. A porous sheet is disposed in an aperture of the outer peripheral frame sheet, and catalyst ink is applied while vacuum-sucking the electrolyte membrane via the porous sheet. The porous sheet protects a coating area where the catalyst ink is applied.